Dealing with Nginx 400 Bad Request HTTP errors
Today I'll write about something I experienced personally, on my websites. Some visitors reported that they were getting a "400 Bad Request" Nginx error randomly when visiting pages. And when they start getting that error, they can't access the site anymore: it'll output the same error no matter the page, until you "clear your cache and cookies". The error is easily understandable and is likely to be caused by... too much cookie data. Every time a visitor loads *any* page/content/file of your website, it sends the cookie data to the server. Cookie data is sent under the form of 1 header line starting with "Cookie: ". Basically, Nginx by default is configured to accept header lines of a maximum size of 4 kilobytes. When a line in the headers exceeds 4 kilobytes, Nginx returns the '400 Bad Request' error. Cookie data sometimes gets big, so it causes the error. It particularly happens on forums like vBulletin, Invision and others...